1. Field of the Invention
The present invention relates to a high-breakdown-voltage semiconductor device in which silicon carbide (SiC) is used as a substrate material.
2. Description of the Related Art
In a semiconductor power device, there are demands for a device structure and a device material for minimizing an on resistance and maximizing a breakdown voltage. Heretofore, to achieve a high-breakdown-voltage, an Si power device is prepared on an Si substrate, and a junction termination structure such as a RESURF or a guard ring is prepared in a device terminal end portion where an electric field is crowded. In respect of cost, there is a demand for a small area in a region required in the junction termination structure.
In recent years, a power device (SiC power device) made of an SiC material has been developed which surpasses performances of a power device made of an Si material by leaps and bounds. Since SiC is a wide band gap semiconductor, and an intensity of breakdown electric field is nearly ten times as large as that of Si, it is possible to improve tradeoff between the breakdown voltage and the on resistance of the power semiconductor device (e.g., “Fundamentals and applications of SiC devices”, by Kazuo Arai, OHMSHA, LTD., Japan, pp 165 to 168).
In respect of quality of an SiC crystal, epitaxial growth of SiC is required in manufacturing an SiC substrate. An epitaxially grown film of SiC is grown on an SiC plane slightly tilted at a crystal angle from a <0001> direction referred to as a c-axis (e.g., U.S. Pat. No. 4,912,064).
However, SiC is an expensive semiconductor material as compared with Si. Therefore, the SiC power device is more disadvantageous than the Si power device in respect of the cost. Furthermore, even in the SiC power device, as well as in an Si power device, an electric field reducing structure is required which is a cause for a cost increase.
As described above, it is expected that the SiC power device can exhibit a performance higher than that of the Si power device, but there has been a problem in respect of the cost. Therefore, there has been a demand for realization of low cost SiC power devices.